Adds configuration option to not require value attributes.

[pelted]

What this does:
Provides a Engine configuration option to require (or not) the value filed for complex vdtp types.

Why?
Some providers are sending NULL values when syncing lists such as phone numbers. Although I agree with the Readme statement:

there's no point being sent (say) an e-mail section which has entries that don't provide the e-mail address!

Unfortunately, if an identity provider is sending NULL rather than omitting the result from a list this provides a way to work around that. We should be using Model validations anyway.

[pond]

I'll have a think about this one - maybe a cleaner fix is to allow those spec-optional things to be optional in the schema, and rely on the gem integrator's model validations underneath as suggested. Otherwise it makes all VDTP types optional which seems a bit broad.

[pond]

Yeah, OK, so fair enough. I see from your description that you're concerned about more than one possible type receiving null in the optional field, so I'll merge this and add a bit of documentation around it too.

This will be in v2.1.0 hopefully released later today (NZ time).

[pond]

Available now in v2.1 (https://rubygems.org/gems/scimitar).